1. FIELD OF THE INVENTION
The present invention relates to pressure controlling devices for regulating the pressure and flow within gas and oil-producing wells. More specifically, the present invention is a choke-type device which maintains bottom hole pressure at a substantially constant level while greatly reducing the amount of sand and water entering the production string.
2. DESCRIPTION OF THE PRIOR ART
Oil and gas well pressure controlling devices are well known in the art. Many different choke-type devices and the like are described in the patent literature. For instance, an early patent, U.S. Pat. No. 216,064, issued Jun. 3, 1879, to Samuel Spencer, describes an apparatus for regulating the flow of oil in wells. The apparatus is placed inside a standard well which includes an outer casing having a perforated lower end, and an inner tube placed inside the outer casing. A packer is placed in the annulus between the outer casing and the inner tube to both force gas and oil into the inner tube and to prevent water from upper strata from contaminating the oil present in the lower reaches of the casing. The apparatus includes a funnel placed within the inner tube, and a standing valve which allows oil to pass upward through the valve, but blocks oil from descending back down the well. The major draw back to this device is that the sand and sediment which passes the standing valve will be lifted to the surface along with the oil, thereby necessitating a subsequent filtration step to remove the sediment from the oil. It is just this step that the present invention aims to eliminate by greatly lessening the amount of contaminants which enter the production string of the well.
U.S. Pat. No. 1,039,496, issued Sep. 24, 1912, to Daniels et al, describes an expanding sleeve for releasably sealing a standing valve within the inner tube of an oil well. The sleeve ensures a snug fit between the inner tube and the standing valve so as to prevent oil from passing around the outer periphery of the standing valve.
H. C. Otis describes a bottom hole choke in U.S. Pat. No. 1,916,070, issued Jun. 27, 1933. The choke includes a releasable closure located at the mouth of the choke, and a passage tube to communicate pressurized gas which accumulates at the top of the well to the bottom of the well. The closure is opened to admit oil into the inner tube, and the passage tube is then opened to allow the pressurized gas from the top of the well to expand into the bottom of the well, This is then utilized to lift the oil to the surface.
U.S. Pat. No. 2,095,899, issued Oct. 12, 1937, to J. R. Yancy, discloses another type of removable bottom hole choke. The choke is preferably formed within a single unitary housing, both to facilitate ease of insertion and removal of the choke, and to ensure a tight fit of the choke within the inner tube. The choke housing also includes an assembly which is matingly engageable with a setting tool for placing and removing the choke from within the inner tube.
Wents et al describe an apparatus for controlling the flow of liquid within a well casing in U.S. Pat. No. 3,136,368, issued Jun. 9, 1964. The apparatus includes a ball trapped within a cage, and a flexible diaphragm disposed within the cage, The diaphragm has an opening therethrough through which the ball can pass if motivated to do so with sufficient force. When the apparatus is lowered into a well, the ball is forced to the upper limit of the cage, and liquid flows freely through the opening in the diaphragm, and around the ball. However, when back pressure is sufficiently high, the ball will be forced against the diaphragm and against the lower limit of the cage, thereby forming a seal to prevent the back flow of liquid down the well.
U.S. Pat. No. 3,189,316, issued Jun. 15, 1965, to D. C. Preston, Jr., describes a sub-surface choke-like apparatus for inducing the flow of fluid in a well. The apparatus is a valve device designed to create a high pressure differential across the perforations at the lower end of the well casing. The high pressure differential causes a sudden flow of liquid from the geological formation into the casing, which clears accumulated silt from the perforations. The silt, which has now entered the production string of the well, is lifted to the surface, where it must be separated from the oil. In contrast to this apparatus, the present invention creates enhanced flow within a well while simultaneously reducing the amount of sand, silt and water entering the production string. While the Preston device may enhance liquid flow, it will also increase the amount of sand lifted to the surface.
U.S. Pat. No. 3,318,386, issued May 9, 1967, to H. U. Garrett et al, describes a well fluid flow regulator. The regulator comprises a pressure sensitive assembly which is placed at the bottom of the well bore. Pressure data from the assembly is used to calculate the back pressure needed to maintain a substantially constant "sand-face differential." The sand-face differential is the pressure gradient from a point within the oil-producing formation to a point within the well casing. Opening and closing of secondary valves in response to the pressure data is used to maintain a constant sand-face differential, which results in more efficient utilization of the oil-bearing formation.
C. C. Brown describes a check valve assembly for preventing the reverse flow of drilling fluid down a well in U.S. Pat. No. 3,850,191, issued Nov. 26, 1974. The valve includes a conical valve body, a ball closure which normally rests outside of the flow path of the well, and a seat for the ball. The ball of the valve, normally outside of the fluid flow, is responsive to the rate of reverse flow through the valve body. At a predetermined level of reverse flow, the ball will be urged into the flow path and seat in the valve, thereby preventing back flow down the well.
U.S. Pat. No. 3,941,511, issued Mar. 2, 1976, to Thomas Morgan, describes an apparatus for artificially lifting oil to the surface after the bottom hole pressure has decreased to a point that artificial lift becomes necessary. The apparatus includes an accumulator placed within the lower reaches of the well casing, with the uppermost portion of the accumulator being vented to the surface. A floating piston-type device is positioned above the accumulator, within the production string, and a stinger tube defines a connection between the accumulator and the production string above the floating piston. Pressure applied to the vent line forces oil from the accumulator to the production zone above the floating piston. The piston is then used to lift the oil to the surface. When the piston reaches the top of its flight, additional pressure from the accumulator is vented into the production line to aid in lifting the oil to the surface and to simultaneously relieve pressure from below the floating piston to allow it to sink back to the bottom of the production tubing. The cycle is then repeated.
U.S. Pat. No. 4,036,297, issued Jul. 19, 1977, to Patrick Swihart, Sr., discloses a bottom hole flow control apparatus which modifies well flow in a pulse-flow type manner. Through the cooperation of a piston chamber, production inlet and production outlet chambers, and associated valves, the well can be closed in response to the occurrence of a particular flow rate through the production string. This more effectively utilizes the bottom hole pressure because the well can be "pulsed" to agitate the rising oil, and to close down production flow when flow rates become inefficiently high.
Related choke devices and gravel pack installations are described in U.S. Pat. No. 4,210,208, issued Jul. 1, 1980, to F. E. Shanks; U.S. Pat. No. 4,605,074, issued Aug. 12, 1986, to V. H. Barfield; and U.S. Pat. No. 5,327,960, issued Jul. 12, 1994, to H. M. Cornette et al.
A large number of flow control devices and methods have been described in the foreign patent literature as well, most notably from the former Union of Soviet Socialist Republics. Among these devices is the piping described in SU 190,843, issued Nov. 17, 1967. This reference discloses a set of interlocking pipe string sections in which the central-most section has the widest inner diameter, while both the bottom hole and top hole ends have substantially smaller inner diameters. In flowing through the expanding and then contracting production string, the oil is sharply expanded and contracted, which agitates the oil to extend the natural flow of the well.
The remaining Soviet documents disclose choke apparatuses, check valves, and related flow control devices which are cumulative to the above-discussed references. Included among these Soviet references are SU 1,231,208A, issued May 15, 1986; SU 1,298,334A, issued Mar. 23, 1987; SU 1,375,801A, issued Feb. 23, 1988; SU 1,461,872A, issued Feb. 28, 1989; and SU 1,772,344A; issued Oct. 30, 1992.